Such a steam power plant usually contains one or more circulation-type steam generators having pressure drums with associated heating surfaces. The circulation-type steam generators are used to produce steam, particularly in different pressure stages, which can be fed to a steam turbine or rather the relevant pressure stage of the steam turbine. The steam power plant can also have one or more so-called once-through steam generators, also known as Benson boilers which, however, are mostly incorporated in the high-pressure stage.
Conventionally, steam power plants are more or less heavily drained depending on the operating state of the steam power plant. Draining takes place e.g. during ongoing operation from long-closed pipework in which condensate has collected. For this purpose the relevant pipework is briefly opened, thereby draining it. This means that water is lost from the water circuit and must be replenished by supplying additional water known as deionate. Additional draining occurs during startup or shutdown of the steam power plant, as when the steam power plant is shut down, for example, the steam present in the water circuit gradually condenses and the resulting liquid water must not remain in the system sections, particularly the heating surfaces. During shutdown, more water is drained from the water circuit than is replenished, so that finally no more water is replenished.
It is known to collect the drainings, i.e. to combine them. It is also known to store some of these drainings temporarily in a tank. As the drainings, i.e. the drained water, is conventionally discarded to the environment via a pump, the tank serves only to reduce the operating time and frequency of operation of the pump. It is also known to depressurize the drained water in a separator vessel and to separate the water and steam from one another. The separated steam is then discharged into the environment.
The disadvantage with the prior art is in particular that the expensively produced deionate which is drained off is not returned to the water circuit but is discarded to the environment in the form of waste water. With conventional steam power plants, the deionate costs incurred are significantly increased, particularly in the event of frequent startups and shutdowns. Moreover, the environment is considerably impacted by the heavy waste water discharge. The re-supplied deionate has a high oxygen and carbon dioxide content requiring deaeration of the deionate, which means a longer startup time for the steam power plant.